Shrink selection panel icons
Current gui has no space for more structures/formations to be displayed and some
civilisations are very close to hit this limit.
Alternative would be scrolling option or pages, but until then this is acceptable solution.
Differential Revision: https://code.wildfiregames.com/D2875
Patch by: Nescio
Reviewed by: Angen, geneva55
Comments by: wraitii, Stan